The invention concerns a suction roll for a paper machine and a method for producing a desired pressure profile for a suction roll.
One principal objective in paper manufacture is to achieve a paper product which is as uniform as possible. In drying, a paper web shrinks more in its lateral areas than in its middle area. This may even result in the paper in the lateral areas being unusable because of this shrinkage. To maintain the quality of the paper, it is preferable that the shrinkage of paper be small and uniform.
In prior art methods, attempts have been made to avoid this problem by increasing negative pressure in the suction roll. When the negative pressure is increased, the web shrinks less in the middle area, but the difference in shrinkage between the lateral areas and the middle area may become even larger. Thus, the result is not desirable.